1. Field of the Invention
The present invention relates to a coating material which is applicable for coating on a surface of an aluminum die casting mold, parts of a high temperature sliding member and the like, which are exposed to a high temperature. More particularly, the present invention relates to a coating material including a CrN adhesion layer, a TiAlN/CrN support layer, a TiAl(CrSi)VCN functional layer and the like, and a method for coating the same.
2. Description of the Related Art
As manufacturing processes are becoming automatized, scaled up and sped up in conjunction with industrial development, the con under which various metal materials, such as molds and mechanical structures, used are becoming increasingly rigorous. In particular, high-level physical properties are required for an aluminum die casting mold due to the environment in which such molds are continuously subjected to high loads and high impact. Generally, the lifespan of the mold is determined by the material forming the mold, the mold design, working conditions under which the mold is subjected to, heat treatment and surface treatment of a mold and the like. Further, there is a problem in that the lifespan of a mold is drastically reduced as a result of heat checking caused by thermal impact and generation of sticking and abrasion caused by molten aluminum, a thermal softening phenomenon caused by working at a high temperature, and the like.
Further, the automotive industry is developing various environmentally friendly vehicles with a goal of reducing the amount of carbon dioxide emission to 50 g/km by the year 2020, which is a level of about 35% to 50% of the current level. In order to achieve this goal, efforts to increase combustion efficiency of an engine and reduce NOx and the like have been made.
In order to increase the combustion efficiency and reduce the emission of NOx and the like, an exhaust gas recirculation (EGR) is mounted. The EGR is an apparatus which recirculates a portion of an inert exhaust gas into an intake system, allows the recirculated exhaust gas to be mixed with a mixed gas introduced into the engine, and decreases the maximum temperature during combustion to produce less NOx.
Generally, the EGR includes a flat valve, a shaft, bushing, a washer, a housing and the like, and an actuator outside the housing adjusts the opening and closing of the flat valve. In this case, the flat valve and the bushing or the washer and the bushing slide off at high temperatures.
As a result, it is difficult to open and close the flat valve due to high temperature sticking and high temperature abrasion of the washer or the flat valve and the bushing, and quality problems such as noise generation, output generation and the like occur.
In order to solve the above problems, CrN has been recently applied as a metal coating material. However, since a reduction in hardness occurs due to insufficient thermal resistance at 500° C. or more and a sticking phenomenon occurs during friction and abrasion, there is a problem in that abrasion is accelerated.
In particular, a high level of physical properties are generally required for an aluminum die casting mold due to ultrahigh pressure and high cyclization, and therefore TiAlN or AlCrN and the like have been used as a coating material in the related art.
However, there are problems in that the TiAlN coating material has inadequate thermal resistance for use as a coating material of an aluminum die casting mold, which is exposed to high-temperature conditions of up to 750° C., and further has insufficient thermal stability which results in deterioration in physical properties and the like, when exposed to high-temperature environments. In addition, while the AlCrN coating has relatively excellent thermal resistance compared to the TiAlN coating, it has a very low sticking resistance in that a molten alloy of aluminum and the like easily adheres to the surface of a mold coated with TiAlN. This results in problems, such as a decrease in the lifespan of the mold and a deterioration in the quality of a casting product produced therefrom.